THURSDAY, Aug. 21, 2014 (HealthDay News) -- A combination of therapy and antidepressants appears to best help people with severe but short-term depression, a new study reports.

Four out of five people suffering from severe depression for less than two years experienced full recovery when treated with cognitive therapy plus antidepressant medication, researchers found.

On the other hand, the combination didn't work much better than drugs alone in helping people with mild depression or those with severe and chronic depression lasting longer than two years, said lead author Steven Hollon, a professor of psychology at Vanderbilt University in Nashville.

"For those folks who were more severely depressed but not chronically depressed -- about one-third of the sample -- they were 30 percent more likely to achieve recovery than if they received medications alone," Hollon said. "That's a big, big advantage."

If follow-up studies verify these findings, they could help mental health professionals direct available resources to those who would gain the most from them, said Dr. Scott Krakower, assistant unit chief of psychiatry at Zucker Hillside Hospital in New York City.

"It could help us figure out who needs therapy acutely and who will benefit most from medication, because it's so hard to find a therapist," Krakower said.

When used for depression, so-called cognitive therapy aims to break the pattern of negative thinking. A trained therapist teaches specific skills intended to counter unhealthy thoughts about yourself, your world or your future.

The study, published online Aug. 20 in JAMA Psychiatry, involved 452 adults with depression who received treatment at one of three university medical centers in the United States. They were randomly assigned to receive antidepressant medication alone, or a combination of antidepressants and cognitive therapy.

Doctors were free to switch the patients' antidepressants around until they found the most effective drug treatment for each person, Hollon said.

"We allowed the clinicians to do whatever it took to get the patient better," he said. "We really pulled out all the stops. We did something that was closer to what people would do in good clinical practice in the real world."

The doctors treated the patients until their depression went away, and then kept up treatment for six months. If patients made it six months without relapsing into depression, they had experienced a full recovery, Hollon said.

For those who experienced a full recovery, the combination treatment appeared to help most. About 73 percent of patients who received therapy and medication made a full recovery, compared with 63 percent of patients receiving medication alone, according to the researchers.

Combination treatment particularly helped people with short-term but severe depression, leading 81 percent to full recovery versus 52 percent for those receiving medication alone.

People with mild depression did not get any better help from combination treatment than from drugs alone, nor did people with chronic severe depression, the investigators found.

It's likely that people with mild depression only need medication -- or even the suggestion of medication -- to bounce back and remain healthy, Hollon said.

"For people who have less severe or non-chronic depression, we know you get a very high placebo rate," he said. "Those people do better on anything."

On the other hand, people with deep and long-lasting depression appear hard to reach by any means. "For whatever reason, for people with chronic depression, we haven't found a way to help those people out," Hollon said.

Hollon noted that all depression patients who received combination treatment had fewer serious events -- such as psychiatric hospitalization, medical hospitalization and suicide attempts -- than patients who received medication alone.

"Having the additional therapy component with medication helps patients with depression, clinically," Krakower said. "Medication and therapy should still be used in combination as much as possible, until we know more."

Hollon's team will continue to observe the patients over time, to see how many will be able to remain depression-free for the long term.